PROJECT SUMMARY/ABSTRACT Each year 500,000 patients undergo cardiac surgery in the United States, and acute kidney injury (AKI) complicates recovery in 25% of patients. AKI is associated with subsequent postoperative arrhythmias, wound infections, and sepsis, and independently predicts a 5-fold increase in death at 30 days. Despite advancements in surgical technique and perioperative patient management, cardiac surgery-associated AKI (CSA-AKI) remains a major problem and no therapies have been shown to improve clinical outcomes. While there are many reasons that previous efforts to identify and validate new therapeutic targets for AKI have been unsuccessful, a key feature is that discovery efforts were not primarily driven by human data. Leveraging BioVU (Vanderbilt's large- scale DNA biobank), we performed a Phenome-Wide Association Study (PheWAS) based on ICD billing code and genotype data in a disease-agnostic cohort of ~36,000 patients and identified novel genotype-phenotype associations between single nucleotide polymorphisms in the gene that encodes the protein target of montelukast (CYSTLR1) and AKI phenotypes. Montelukast is an anti-inflammatory leukotriene receptor antagonist that is FDA approved to treat asthma and allergic rhinitis, and inflammation is a mechanism of AKI. In additional preliminary studies montelukast reduces renal injury in preclinical models, urinary concentrations of leukotrienes increase significantly during cardiac surgery and more so in patients who develop AKI, and patients taking montelukast have a 38% reduction in AKI over time compared to patients not taking montelukast. To determine if montelukast can be repurposed to prevent CSA-AKI and potentially other forms of AKI in subsequent initiatives, we will first perform a phase II trial to measure the effect of montelukast on CSA-AKI and assess any safety events. To properly design and execute this phase II trial we assembled a multidisciplinary team of physician scientists and staff with the relevant expertise and experience to accomplish four specific aims: (1) Determine study cohort availability and baseline characteristics by simulating study cohorts using VUMC's Synthetic Derivative; (2) Determine optimal montelukast dosing regimen and refine the trial's mechanistic studies by measuring LTC4, LTD4, and LTE4 leukotriene subtypes in urine of patients who did and did not develop AKI in a previous study; (3) Optimize study design to most efficiently recruit patients and test the hypothesis; and (4) Complete all study startup tasks. The successful completion of this project will allow us to commence the clinical trial immediately. Proving that a safe, affordable, generic drug can be used to prevent CSA-AKI is a major priority. In addition, demonstration that the published and publicly available computational PheWAS algorithm is an effective tool for drug repurposing will lead to additional medical treatments.